In this study, the thermal conductivity of form-stable phase change materials (PCMs) is improved by the addition of graphene nanoplatelets (GNPs). In the first step, the dispersed GNPs were mixed with palmitic acid (PA) particles using an ultra-sonication method. Then, the prepared material was added to form-stable phase change materials (PA/PPy) obtained by a polymerisation technique. The amount of PA particles remained constant in the prepared form-stable phase change materials. FT-IR and SEM analyses were used to investigate the structure and surface morphology of form-stable PCMs, respectively. The thermal properties, stability and conductivity of the materials were also characterised using DSC, TGA and thermal conductivity analysis, respectively. The results indicated that GNPs had a significant effect on improving the thermal conductivity of form-stable PCMs (PA/PPy). By doping 1.6% of GNPs, the thermal conductivity and thermal capacity of PA/PPy/GNPs form-stable PCMs could reach up to 0.43 W/m K and 151 J/g, respectively. In other words, thermal conductivity increased by 34.3% in comparison with PA/PPy form-stable PCMs. The prepared PA/PPy/GNPs form-stable PCMs are anticipated to show improved performance for solar thermal energy storage applications. (C) 2015 Elsevier B.V. All rights reserved.